Question Computer keeps restarting for a while, then it doesn't power on anymore, until i leave it overnight

Jan 25, 2020
Background: First of all, this is an old custom built pc so all warranties should be gone. I'm nothing near expert, I just picked my own parts and had someone put it together for me, somehow i managed to troubleshoot my pc problems over the years.
A lot of issues over the years, but I somehow managed to get it working like reseating, dusting, reapply thermal paste, fixing bent CPU pins, changed motherboard once only because i couldn't figure it out and pc repair shop said it was dead, and it worked fine after that change

Problem: When pc is left untouched overnight, it does turn on, but after a while it just dies like totally then after a while it reboots back up.
When it turns on, I login and try to update windows 10 from 1903 to 1909, but pc was never on long enough to complete.
After a few reboots (nothing to do with update), after the power cuts, the pc doesnt reboot anymore and stays dead, tried for 3~4 days now, same situation every day

Motherboard: Asus P8Z68-M PRO
CPU: Intel i5 3470
CPU heatsink and fan: Cooler Master ( not sure the model but don't think it matters)
PSU: Cooler Master GX bronze 550W
SSD: Samsung 850 EVO 250GB
GPU: AMD Sapphire HD 7850 2G GDDR5
RAM: Kingston 4GB + Strontium 4GB

What I have tried
  1. Reseated both ram in all 4 slots, and with 1 ram only
  2. Combination of removing CMOS and jumping
  3. Reapplied thermal paste to CPU and GPU, reseating heatsink
  4. Checked the cables for proper seating, except those coming from psu
  5. Dusting everything, including opening psu ( tons of dust, which I thought caused shorting)
Possible problems
  1. PSU, did the paperclip test some time ago, it works, but read online test not conclusive, not sure how to go from there other then get a new one
  2. Motherboard, though it looks fine from the surface
  3. Drivers, windows version is 1903 instead of 1909. I recently reinstalled AMD driver but my AMD audio driver is gone after I accidentally deleted it in device manager to tried to uninstall and let windows reinstall. Rest of the pc drivers I have not been regularly updating it
  4. Malware/ Virus, Ran my ESET antivirus, but pc keeps rebooting after a few mins, so that doesnt help
  5. Overheating, using openhardwaremonitor, motherboard temp #1 is at 60°C after reboot, but not sure what thing that temp is referring to.
Into my bios, cpu fan is sometimes red below 600 rpm, but sometimes is normal at 700+rpm, not sure if that causes the overheating, and if that fan refers to the cpu heatsink fan

GPU in some months ago overheats when playing games, and causes shutdown reapplied thermal paste and it's good now but not sure what to do if it still overheats, but definitely not for this problem as I haven't played any games and temp is at 32°C

Any help is much appreciated, thanks a lot
Jan 25, 2020
Hi, I've sent it to a repair shop for diagnostic test and below are the results; please advise if I should go for those models/ brand or should i buy the parts myself;

1) Your mainboard is faulty, it will cause your desktop to intermittently unable to power on.
The charges for mainboard replacement as shown:
a) GIGABYTE LGA1155 MAINBOARD GA-H61M-S2PH (3 years warranty)-SGD 129

2) Your graphic card HD 785(benchmark 3849) is faulty. The options for replacement of the graphic card as shown:
a) Gigabyte GT 710(3 year warranty)-SGD95, benchmark 688
b) Gigabyte GeForce GTX 1650 4GB(3 year warranty)-SGD275, benchmark 7949

On top of the repair, there is a service repair(1 year warranty)-SGD85

Since I'm changing my motherboard, should I go make my PC up to the latest stuffs? My current one, for example supports up to DDR3 ram only, so the new one should at least support DDR4, I don't mind spending a bit more(like getting better GPUs) , since it is like a "new system" anyways, just that I can save some money reusing old parts.

For GPU, I want something better than my current model, is AMD RX 570 better? If not, I'm thinking GTX 1660 or GTX 1650 super or RX 5700 or RX 5600XT or RX 570

Please also let me know which old parts I cannot use for a new build, even if it is working, or highly recommended to upgrade ( such as psu voltage)

Thanks a lot.